What are polyamides (PA)?

Polyamides are semi-crystalline thermoplastics with a crystallinity of up to 60%. They are produced by polycondensation of an amino and a carboxylic acid group, often using aminocarboxylic acids directly as monomers, which contain both groups. Polyamide is an umbrella term and there are many different types, depending on the monomer used. The types are usually labeled with PA and a number, where the number corresponds to the number of carbon atoms in the monomers. PA 6, for example, is made from a single monomer, caprolactam, with a carbon chain of 6. PA 6.6, on the other hand, is made from two monomers (hexamethylenediamine and adipic acid), each with 6 carbons. The most important types are standardized in DIN EN ISO 1043-1. All polyamides have a high water absorption (up to 3.5 %), which also ensures very good impact strength, rigidity, abrasion resistance and sliding properties. Due to the combination of good water absorption and good damping properties, PAs are often used in damping technology. Polyamides are generally resistant to solvents, hydrocarbons, oils, petrol and greases. They are susceptible to acids, strong alkalis and oxidizing agents. With the exception of impact strength, most properties can be improved by glass fiber reinforcement. PA 66 has even better hardness and heat resistance, making it particularly suitable for use at high temperatures. In general, the upper continuous service temperature is 80 – 150 °C, depending on the material. PA 610/612/11 and 12 have a slightly poorer water absorption and therefore a lower hardness. PA 6-3-T is one of the few amorphous polyamides, which means that the listed properties can be combined with transparency, but at the same time the susceptibility to stress cracking also increases. PA6, PA6.6 and PA12 are also available glass fiber reinforced (PA GF), which improves some mechanical properties. Polyamides are used in mechanical engineering, vehicle construction, electrical engineering and sanitary engineering.